Process for the preparation of aliphatic ethers



United States Patent PROCESS FOR THE PREPARATION OF ALIPHATIC ETHERSRichard Leonard Kronenthal, Fair Lawn, N. J., assignor toColgate-Palmolive Company, Jersey City, N. L, a corporation of DelawareNo Drawing. Application September 14, 1955, Serial No. 534,393

7 Claims. (Cl. 204-59) The present invention relates to a process forpreparing aliphatic ethers. More particularly it relates to thepreparation of aliphatic ethers by electrolysis of aliphatic carboxylicacid salts.

It has previously been proposed by Kolbe to electrolyze aqueoussolutions of aliphatic carboxylic acid salts to produce hydrocarbonsaccording to the overall equation:

It has also previously been proposed to electrolyze alcoholic aqueoussolutions of aliphatic carboxylic acid 2 .1

salts under certain special conditions so as to prepare mixtures ofalcohols and olefines which contain one less carbon atom than theoriginal salt from which they are prepared.

It has now been discovered that electrolysis of aliphatic phatic etherscomprise electrolyzing, using a graphite anode, a substantiallyanhydrous solution of aliphatic carboxylic acid salt containing morethan one carbon atom in a solvent therefor selected from the groupconsisting of lower monohydric and dihydric alcohols, and recovering analiphatic ether of a carbon content equal to one less than the sum ofthe carbon contents of said aliphatic carboxylic acid salt and saidalcoholic solvent. This electrolysis is preferably carried out usingrelatively low current densities, and dilute anhydrous alcoholicsolutions of aliphatic carboxylic acid salts in the presence of stable,electrically conductive inorganic salts as set forth in detail below.

It is essential to the present invention that electrolysis be carriedout under anhydrous or substantially anhydrous conditions, as thepresence of relatively small proportions, e. g. about 10% of water,results in a marked decrease in the yield of the instant ethers.

The alcoholic solvent employed in carrying out the present process isselected from the group consisting of lower monohydric and dihydricalcohols containing up to about 3 carbon atoms, e. g. methanol, ethanol,ethylene glycol, and the propanols. In general it has been found thatexcellent yields are realized when using methanol, probably because ofits stability and superior solvation characteristics. Good yields mayalso be obtained when ethylene glycol is used, however under unfavorableconditions some oxidation, e. g. to glycol aldehyde, is experienced.

The alcoholic solvents are used in considerable excess. Preferably,solutions to be electrolyzed are less than about 0.5 to 0.75 molar withrespect to the aliphatic carboxylic acid salt, as at higherconcentrations considerable amounts of the Kolbe hydrocarbon form. Inthe case of potassium laurate dissolved in methanol, the maximum yieldsof l-methoxyhendecane have been found to occur when the solvent is 0.335molar or less in potassium laurate.

The aliphatic carboxylic acid salts employed in the instant novelprocess are metallic salts of saturated or unsaturated aliphaticcarboxylic acids containing more than one carbon atom. These salts maybe pure or in admixture, however it is essential that they have at leastslight solubility in the alcoholic solvent used. Suitable carboxylicacid salts for carrying out the present invention include the alkalimetal salts such as sodium propionate, potassium caprylate, sodiumlaurate, sodium myristate, potassium oleate, potassium stearate and thepotassium salts of tridecanoic acid, pentadecanoic acid and margaricacid. While free aliphatic carboxylic acids are not suitable to initiatethe instant process, they may be added after electrolysis has commencedusing carboxylic acid salt. On such addition, the free acid will reactwith metal hydroxide liberated at the cathode to form metal salt whichwill then enter the electrolysis reaction.

It is a preferred embodiment of the invention to carry out the instantelectrolysis in the presence of electrically conductive inorganic salts,e. g. ionically bonded inorganic salts, stable in the electrolysismedium. The particular salt employed is not critical, suitable saltsincluding for instance the alkali metal chlorides, sulfates andpersulfates. Specificexamples thereof are potassium andsodium-chlorides, -sulfates, and -persulfates. The salts are generallyemployed by preparing a saturated solution or suspension thereof in thealcoholic solvent which is used.

While the use of these inorganic salts somewhat diminishes the currentefiiciency of the electrolytic system employed, their presence isessential to the procurement of high yieldsof ether and suppression ofside reactions. Thus it has been found that whereas in the presence ofsuch salts, relatively high yields may be realized, a similar processcarried out 'in the absence of such salts results in the production of aproduct consisting of about only one-third ether and two-thirdshydrocarbons. Coating of the carbon anode is also experienced in theabsence of .these salts, and the coating must be periodically scraped tomaintain the desired current density.

The yield of ether obtained is further influenced by the current densityemployed in the electrolysis cell, i. e. current densities up to about40 amperes per square decimeter of anode surface favoring the productionof ethers. Although the instant ethers are also generated at highercurrent densities, side reactions such as the Kolbe reaction becomeincreasingly prevalent under such conditions.

It is essential that graphite be employed as the anode material.Substitution of another material therefore, e. g. platinum, results inthe production of products lacking any analytically detectable amountsof ether. A large variety of materials are suitable for use as cathodes,suitable substances being platinum, stainless steel, carbon, copper,silver, nickel and the like.

The following examples are given to additionally illustrate the natureof the invention and it will be understood that the invention is notlimited thereto.

EXAMPLE I 1 -methaxyhendecane A direct current of 3.5 amperes at apotential of volts is passed through 200 ml. of a well stirred,refluxing methanolic solution containing 16.0 grams (0.067 mole) ofpotassium laurate and 2 grams of potassium chloride for 6.5 hours. Theanode is a graphite cylinder having a surface area of 0.1 squaredecimeter, thus the current density is 35 amperes per square decimeter.The cathode is a coiled platinum wire.

The electrolyzed reaction mixture is poured into 600 ml. of water andextracted three times with diethyl ether. The combined extracts arewashed once with water and dried over anhydrous magnesium sulfate.

The dried ethereal solution is then concentrated and rapidly distilled,yielding 12.0 grams of material boiling from 40 to 85 C. (0.25 mm.).Rough fractionation of this distillate gives three major fractions. Thefirst fraction amounts to 1.75 grams and is predominantly 1- hendecene.The second fraction amounts to 6.75 grams and is predominantlyl-methoxyhendecane. The third fraction 2.25 grams is predominantlymethyl laurate. The l-methoxyhendecane fraction is identified byinfrared analysis by comparison with l-methoxyhendecane prepared byreacting methyl sulfate with the sodium alcoholate of hendecanol.

The combined aqueous residues are acidified and the residual ether isthen removed on a steam bath. No lauric acid is thus recovered,indicating that all of the potassium laurate starting material has beenconsumed.

EXAMPLE II Z-hendecyloxyethanol A solution of 16.0 g. (0.067 mole) ofpotassium laurate and 4.0 g. of potassium chloride in 190 ml. ofethylene glycol is subjected to electrolysis at 110 volts, 3.5 amperesat 70100 C. for 6.5 hours. The cathode and anode are as described inExample I above. The reaction mixture is worked up as described inExample I and yields 5.0 g. of Z-hendecyloxyethanol, B. P. 90ll5 (0.25mm.), most at 115, which crystallizes in ice water. The acidifiedaqueous residue yields 6.8 g. of lauric acid.

While there has been disclosed and described what is at presentconsidered to be the preferred embodiment of the invention it will beunderstood, of course, that many changes, modifications, andsubstitutions may be made therein without departing from the true scopeof the invention as defined in the appended claims.

What is claimed is:

l. A process for the preparation of aliphatic ethers which compriseselectrolyzing, using a graphite anode, a substantially anhydroussolution of aliphatic carboxylic acid salt containing more than onecarbon atom in a solvent therefor selected from the group consisting oflower monohydric and dihydric alcohols, and recovering an aliphaticether of a carbon content equal to one less than the sum of the carboncontents of said aliphatic carboxylic acid salt and said alcoholicsolvent.

2. A process for the preparation of aliphatic ethers as set forth inclaim 1 wherein said solvent is methanol.

3. A process for the preparation of aliphatic ethers as set forth inclaim 1 wherein said solvent is ethylene glycol.

4. A process for the preparation of aliphatic ethers which compriseselectrolyzing, using a graphite anode, a substantially anhydroussolution of aliphatic carboxylic acid salt containing more than onecarbon atom in a solvent therefor selected from the group consisting oflower monohydric and dihydrie alcohols, said electrolysis being carriedout in the presence of an electricaliy conductive inorganic salt, andrecovering an aliphatic ether of a carbon content equal to one less thanthe sum of the carbon contents of said aliphatic carboxylic acid saltand said alcoholic solvent.

5. A process for the preparation of aliphatic ethers as set forth inclaim 4 wherein said solution is less than about 0.5 to 0.75 molar withrespect to aliphatic carboxylic acid salt.

6. A process for the preparation of l-methoxyhendecane which compriseselectrolyzing, using a graphite anode, an anhydrous solution ofpotassium laurate in methanol, said electrolysis being carried out inthe presence of potassium chloride, and recovering l-rnethoxyhendecaneas a product of said electrolysis.

7. A process for the preparation of 2-hendecyloxyethanol which compriseselectrolyzing, using a graphite anode, an anhydrous solution ofpotassium laurate in ethylene glycol, said electrolysis being carriedout in the presence of potassium chloride, and recoveringZ-hendecyloxyethanol as a product of said electrolysis.

References Cited in the file of this patent Glasstone et al:Electrolytic Oxidation and Reduction (1936), pp. 289290.

1. A PROCESS FOR THE PREPARATION OF ALIPHATIC ETHERS WHICH COMPRISES ELECTROLYZING, USING A GRAPHITE ANODE, A SUBSTANTIALLY ANHYDROUS SOLUTION OF ALIPHATIC CARBOXYLIC ACID SALT CONTAINING MORE THAN ONE CARBON ATOM IN A SOLVENT THEREFOR SELECTED FROM THE GROUP CONSISTING OF LOWER MONOHYDRIC AND DIHYDRIC ALCOHOLS, AND RECOVERING AN ALPHATIC ETHER OF A CARBON CONTENT EQUAL TO ONE LESS THAN THE SUM OF THE CARBON CONTENTS OF SAID ALIPHATIC CARBOXYLIC ACID SALT AND SAID ALCOHOLIC SOLVENT. 